Switching mode power supply with alternating current input is a typical electronic system, which has a wide range of applications, and a number of the switching mode power supply applied in the application is great. Most of the input rectifier filter in the internal thereof consists of uncontrolled rectifier circuits and capacitor filter circuits composed of diodes. Due to this, the problems of harmonic pollution and lower power factor of the switching mode power supply are generated. In order to improve the efficiency of the switching mode power supply and reduce the grid pollution, the power factor correction technology is increasingly becoming a hot topic in the power supply design field.
In the switching mode power supply, any circuit that makes the input grid current be non-sinusoidal, or makes the sine wave and the sinusoidal input voltage be in different phases, or makes the input current have harmonic will reduce the power factor PF, thereby resulting in power loss. The use of the power factor correction controller (PFC) is one of the most effective methods to improve the power factor of electronic products and reduce harmonic interference. The broken line in FIG. 1 shows the output terminal voltage waveform of the bridge rectifier of the input terminal grid; the solid line shows the output terminal current waveform of the bridge rectifier of the input terminal grid. As shown in the figure, the outputted current waveform has a serious distortion, meanwhile, the power factor is much low. The waveforms shown in FIG. 2 are the input voltage waveform and the current waveform after using the power factor correction controller, the broken line therein shows the output terminal voltage waveform of the bridge rectifier of the input terminal grid; the solid line shows the output terminal current waveform of the bridge rectifier of the input terminal grid. The output current waveform strictly follows the input voltage waveform; the power factor is close to 1.
However, currently, there is no effective output over-voltage protection function or only a single static over-voltage protection in the power factor correction controller. For the power factor correction controller without output over-voltage protection function, the internal electronic components may be burned when the output voltage exceeds the rated value; for only a single static over-voltage protection in the power factor correction controller, when the load changes, the irreversible damage to the electronic components may be caused when the output voltage instantaneously rises over the rated value. Accordingly, when the output voltage of the power factor correction controller exceeds the rated value (static or dynamic), the protection circuit should provide an effective protection for the electronic components, which is the problems desiderate to be solved.